1. Field of the Invention
The present invention relates to a recording method and a reproducing method of error-correction-coded information.
2. Description of the Related Art
An example of data to be recorded on optical discs such as CDs and DVDs is data which is error-correction-coded using an error correction code such as a Reed-Solomon code or the like (see, for example, Japanese Laid-Open Patent Publication No. 8-125548). For write once and rewritable discs, address information recorded by a wobble form of a track is also error-correction-coded. For example, for wobble addresses (ADIP: ADress In Pregroove) for DVD+RW discs, a shortened Reed-Solomon code RS (13,8,6) is used.
For recording information on a write once or rewritable disc, information needs to be recorded at a correct position. If information is recorded at an incorrect position, information may not be correctly reproduced or information already recorded may be erased, for example. In order to avoid this, address information recorded by wobbling of the track needs to be correctly detected. One method for realizing this is to improve the correction capability of an error correction code (to increase the number of parities added to the address information).
A Reed-Solomon code used for a DVD+RW disc is a code on Galois Field GF (24) and so has a maximum code length of 15. Therefore, without being shortened, the number of parities can be increased by 2 symbols, and a Reed-Solomon code RS (15,8,8) can have a correction capability improved by 1 symbol.
With reference to FIG. 1A, error-correction-coded address information will be described. Address information 10 represented by eight symbols (A0, A1, A2, A3, A4, A5, A6, A7) is error-correction-coded by a Reed-Solomon code RS (15,8,8) to generate coded information 11 including added seven parity symbols (A8 through A14). Here, the symbols of the coded information 11 will be represented by E0 through E14. The coded information 11 is recorded on an optical disc (information recording medium) using a known system, for example, ADIP used for a DVD+RW disc.
For reproducing the address information, as shown in FIG. 1B, the information is reproduced from the optical disc to obtain reproduction coded information 12. The reproduction coded information 12 is obtained by reproducing the coded information 11 recorded on the optical disc. This reproduction coded information 12 is error-corrected to reproduce the address information 10. By the error correction in this example, errors within three symbols are corrected.
When AUX (AUXiliary) in ADIP is used as a parity to generate a Reed-Solomon code RS (13,6,8), the correction capability of the error correction code can be improved without changing the code length thereof. In this case, the address information can be detected more correctly by only changing the format of an error correction coding section.
However, when a new format disc in which the correction capability of the error correction code is improved using the Reed-Solomon code RS (13,6,8) is reproduced by a conventional recording/reproducing apparatus (an apparatus not compatible to the new format but compatible to the DVD+RW (old format)), there is a high possibility that an incorrect address is reproduced because the format of the error correction section is different, although a code word can be reproduced from a wobble reproduction signal because the modulation method is common.
For example, for moving an optical spot to a position close to an address A, the optical spot is usually allowed to reach such a position close to the address A in the following procedure: “the current address is obtained and converted into a radius” to “the optical spot is moved by the difference between the obtained radius and the radius of the address A” to “the post-movement address is obtained and converted into a radius” to “the optical spot is confirmed to be in the vicinity of the address A and the procedure is finished”. When the optical spot cannot move to a position close to the address A by one movement, substantially the same operation is repeated until the above procedure is finished.
For moving the optical spot from an address B at around a radius of 50 mm to an address A at around a radius of 40 mm, the optical spot is usually allowed to reach a position close to the address A by the following procedure: “the current address B is obtained and the optical spot is found to be at a position of the radius of 50 mm” to “the optical spot is moved inward by 10 mm, which is the difference from the address A” to “the post-movement address is obtained and the optical spot is confirmed to be in the vicinity of the address A”.
However, if the pre-movement address B is incorrectly obtained as being around a radius of 25 mm, the optical spot is moved outward by 15 mm. Since the disc has a radius of only 60 mm, the optical spot goes outside the disc. In order to return the optical spot, it is necessary to move the optical spot to a certain area of the disc, perform focusing control or tracking control, then obtain the current address of the optical spot again and move the optical spot. Even if the optical spot is successfully moved to a position around a radius of 40 mm, if the address obtained as a post-movement address is incorrect, the optical spot may be repeatedly moved by the difference from the address A many times.